The Role of Oil in Protein Crystallization - Molecules: Nucleation, Aggregation and Crystallization - page 130

When trying to crystallize a protein, the initial aim of the crystallizer
is to screen rapidly numerous conditions with a minimum of labor, and
using as little material as possible.
To ease the laborious and time-consuming task of crystallization,
an automated technique known as microbatch crystallization was
developed at Imperial College in 1990, which fulfils the following
requirements:

(a) dispensing of very small samples,
(b) high level of accuracy,
(c) rapid screening to determine solubility properties,
(d) homing in on conditions that produce crystallization,
(e) automatic execution in a quick and simple way, and
(f ) flexible changes of operation mode for different types of survey.

To reduce the consumption of material, very small samples must be
dispensed. This leads to two major problems: (a) evaporation and (b) inac-
curacy of dispensing.

The Microbatch Techniques

The problem of evaporation is solved by dispensing and incubating the
crystallization samples under oil, while high accuracy is achieved by
using a micro-dispenser (IMPAX, sold by Douglas Instruments, UK)
comprising a bank of Hamilton syringes driven by stepper motors under
computer control to set up the samples for crystallization. The compo-
nents of the trial (protein, precipitating agents, etc.) are mixed in their
final concentrations, and a specially designed multi-bore microtip
allows very small volumes (0.5 l or less) to be dispensed ready mixed

and with good precision. The crystallization samples are typically dis-
pensed into paraffin-filled microtitre plates. The oil used is paraffin liq-
uid light (density

µ

0.83 g cm −3 ), a purified mixture of liquid saturated
hydrocarbons obtained from petroleum (Molecular Dimensions UK,
Cat. no. MD2-03). Paraffin was chosen after trying a variety of oils,

ρ∼